Is this engine description correct?
 

http://www.ebay.com/itm/Continental-...086419&vxp=mtr

In the description the seller says it is off of a C-336, but it is rated at 210hp. I thought the C-336 used a 195hp version of the engine?

Could you take this and swap it out for the rear engine on a C-337 (NA, of course)?

You can not use this engine in a C337 as is. If you look at the type certificate it says (using C337 or C337A for example):
Engines (Front) Continental IO-360-C or -G or -CB or -GB
(Rear) Continental IO-360-D or -C or -G or -DB or -CB or -GB

Check the type certificate for your specific aircraft.
C337 type certificate

Here is the type certificate and data on the IO360:
IO360 type certificate

Here is some history on the io360:
http://en.wikipedia.org/wiki/Continental_IO-360

IO360 tc says:
The Model IO-360-D is similar to IO-360-A except for rating and oil cooled pistons.

I'm pretty sure the pistons are oil cooled by oil being sprayed on to them via a spray nozzle which is part of the engine case. So it would be a big deal to modify this.

I've attached a picture that shows the nozzles in the crankcase. Hope this helps.

Thanks, Tony!

An interesting comment by the seller...the engine has been stored since 1991. I would be very leery of internal corrosion some place, even though he says "it was oiled up". The pictures of it sure make it look a bit "rough".